Photodynamic Therapy (PDT) uses specifically designed drugs such as Foscan.RTM. (Scotia Pharmaceuticals), ALA (DUSA) and Photofrin (QLT Phototherapeutics) to destroy rapidly dividing cells. These drugs are selectively retained or generated at rapidly dividing cells and are subsequently excited by light to produce the desired effects. The primary mode of activity usually involves energy transfer from these photoexcited drugs to O.sub.2 to produce superoxides or O.sub.2 in its singlet state. To date this excitation has been provided by lasers, lamps, and new materials such as LaserPaint.TM. (laser action in amplifying scattering media). Some of these sources are generally expensive and require complicated delivery systems.
Two of the most important photodynamic therapy drugs are the naturally occurring ALA compound and Photofrin. Both of these are porphyrin compounds that have a peak absorption at 630 nm with a linewidth of approximately 35 nm.
Photofrin has recently received FDA approval for the treatment of esophageal cancer. As such, a low cost optical source at 630 nm has become a very important goal.
FIG. 1 illustrates a conventional optical source 1 that is suitable for use with Photofrin and similar photodynamic therapy drugs. The source 1 includes a pulsed (e.g., 150 nanosecond pulse width, 25 KHz pulse repetition rate) Nd:YAG laser 2 that outputs 1.064 .mu.m light to a frequency doubler, such as a KTP crystal 3. A 532 nm output of the KTP crystal 3 is used to drive a dye laser 4, which provides the desired 630 nm light at the required power.
As those skilled in the art will appreciate, the use of the dye laser 4 has a number of disadvantages, including high initial and operating expense, a required use of fluids, pumps and plumbing, and a frequent need for service.
A number of additional photomedicine applications use laser treatment techniques. For example, U.S. Pat. No.: 5,735,844, issued Apr. 7, 1998, entitled "Hair Removal Using Optical Pulses", by Anderson et al., discloses the use of light energy to remove hair follicles within a skin region. U.S. Pat. No.: 5,707,403, issued Jun. 13, 1998, entitled "Method for the Laser Treatment of Subsurface Blood Vessels", by Grove et al., discloses positioning a laser so that light from the laser impinges a selected area of a patient's dermis to selectively destroy blood vessels at a selective depth. Grove et al. further disclose photomedicine applications including the removal of port wine stains, leg veins and hair follicles. Additionally, U.S. Pat. No.: 5,217,455, issued Jun. 8, 1993, entitled "Laser Treatment Method for Removing Pigmentations, Lesions, and Abnormalities from the Skin of a Living Human", by Tan, discloses a laser treatment technique in which successive irradiations of a treatment site on the skin of a patient is performed to remove, in one embodiment, pigmentations representing a tattoo.
It can be appreciated that in each of the above mentioned photomedicine techniques, and others, a low cost, reliable laser source is beneficial. Similarly, it would be beneficial for a single laser system to deliver light having a range of wavelengths over a range of pulse durations.